Molecular phylogenetic relaionships of unicellular green algae, Chlorellales and its relaives.

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18SrDNA sequece data of 33 species of unicellular green algae, indluding the Chlorellales (sensu Bold & Wynne 1978) (12 species), Chlamydomonadales (3), Tetrasporales (2), Chlorococcales (6), Chlorosarcinales (8), Chaetophorales (1) and Chaetopeltidales (1), were analyzed phylogenetically.1) The Chlorellales is polyphyletic, and the algae of this order distribute in the chlorophycean and trebouxiophycean clades. Number of species of the latter clade is more than the former.2) Biflagellate members whose basal body orientation is clockwise are divided in the Tetracystis-, Dunaliella-, and Volvox-clade. Tetrad formers of the Chlorosarcinales are included in the Tetracystis-clade, being separated from sarcinoid formers of the order. Difference between Dunaliella-clade and Volvox-clade may be caused by their naked and thin-walled swarmers respectively.3) From analysis of quadriflagellate wall-less green algae, it was concluded that the cell wall occurred several times in separate phylogenetic lines, and we proposed a new order Oltomannsiellopsidales.4) A marine chlorococcalean species of the genus Neochloris is obviously a ulotrichalean alga of the Ulvophyceae, and we proposed Pseudoneochloris marina gen.et sp.nov.5) For a marine chlorosarcinale an species of the genus Chlorosarcinopsis, we proposed to establish a new genus in the Ulotrichales, Ulvophyceae.6) Palmophyllum, a species of the Tetrasporales with gelatinous matrix around cells living on rocks in bottom of sea water, is demonstrated to be most related with Prasinophytes.